Thanks to all the info I found on here I have IDed my speedometer issue on my 1994 Bronco. Bad LG/B wire and bad 4WABS module. I jumpered the connector and got my speedo to run after jumpering the LG/B wire to the connector from the VSS. My question now is, can you leave the 4WABS connected to the connector and jumper the same wires outside the box. In other words I do not care if I have ABS or no. Just wondering if jumpering while having the 4WABS still connected would mess up anything else. Thanks up front for your response.
prchrman
jumper + active 4WABS?
I have a 94 w/5.8 & E4OD with the same issues of intermittent hard shifting and cruise control operation. Last week i did the 4WABS jumper (with the 4wabs unplugged) which solved 90% of the hard shifts. Yesterday I realized that my jumpers were a little loose so I found some wire that fit in snug and redid the jumpers. That fixed 100% of the problem! If anyone else is doing the jumper/bypass be sure not to make the same mistake as me because a little bit of play in the jumper will cause the same symptoms as a bad vss.
Since the jumpers solved the problem + my current 4wabs module is working fine (aside from it apparently degrading my vss signal) + I like antilock brakes, i really want to reconnect the 4wabs module. Has anyone heard of any problems in keeping the module active with jumpers installed? Maybe i have seen too many episodes of '1000 ways to die' but i can imagine a freak scenario where an erroneous triggering of a dump valve could occur.
Also, in the diagnostics it says that radio frequency interference is a possible cause yet i havnt heard a case of RF actually being the direct culprit. It does sound plausible because were talking about a very weak analog AC signal being generated by the VSS and its got to be vulnerable to interference. Is it possible that the 4wabs module is actually fine and the ground jumper from pin 21 to 14 is simply reducing interference enough to allow the VSS signal to propagate further downstream to the PSOM, PCM, E4OD and CC?
On a slight tangent: anybody here ever done surgery on a 4wabs unit?
I cant thank Steve83 and Miesk5 enough for the wealth of knowledge that they have contributed here!
![Image]()
I have a 94 w/5.8 & E4OD with the same issues of intermittent hard shifting and cruise control operation. Last week i did the 4WABS jumper (with the 4wabs unplugged) which solved 90% of the hard shifts. Yesterday I realized that my jumpers were a little loose so I found some wire that fit in snug and redid the jumpers. That fixed 100% of the problem! If anyone else is doing the jumper/bypass be sure not to make the same mistake as me because a little bit of play in the jumper will cause the same symptoms as a bad vss.
Since the jumpers solved the problem + my current 4wabs module is working fine (aside from it apparently degrading my vss signal) + I like antilock brakes, i really want to reconnect the 4wabs module. Has anyone heard of any problems in keeping the module active with jumpers installed? Maybe i have seen too many episodes of '1000 ways to die' but i can imagine a freak scenario where an erroneous triggering of a dump valve could occur.
Also, in the diagnostics it says that radio frequency interference is a possible cause yet i havnt heard a case of RF actually being the direct culprit. It does sound plausible because were talking about a very weak analog AC signal being generated by the VSS and its got to be vulnerable to interference. Is it possible that the 4wabs module is actually fine and the ground jumper from pin 21 to 14 is simply reducing interference enough to allow the VSS signal to propagate further downstream to the PSOM, PCM, E4OD and CC?
On a slight tangent: anybody here ever done surgery on a 4wabs unit?
I cant thank Steve83 and Miesk5 enough for the wealth of knowledge that they have contributed here!
No, the VSS isn't that close to borderline; and the wiring for it is an unshielded twisted pair, so RFI should be negligible regardless of chassis & power grounds. I have to think that every instance of poor/no VSS being cured by jumpering out the 4WABS is entirely due to a dead 4WABS module.
I don't know the logic or circuitry of the module, or why it has to output the VSS on a different circuit, but I assume splicing those circuits together with jumpers would cause some problem. I don't THINK it would be a life-threatening problem, but why risk it? There are plenty of '94-96 Broncos in the JYs that you could get a decent used module from, and then you could dissect your original.
I don't know the logic or circuitry of the module, or why it has to output the VSS on a different circuit, but I assume splicing those circuits together with jumpers would cause some problem. I don't THINK it would be a life-threatening problem, but why risk it? There are plenty of '94-96 Broncos in the JYs that you could get a decent used module from, and then you could dissect your original.
Thanks Steve, I think that the used/salvaged option is best considering the alternatives. I guess I'd be able to try out 2 or 3 salvaged ones for the price of paying for a module rebuild. Plus I'd be able to dissect that bugger after I get a working replacement.
Since I cleaned up my jumpers this time last night, I have made 8 trips that covered 40 miles of city traffic. The whole time every shift was perfect, way better than at any time since I got the truck a year ago. However, there was one exception that is making me consider doing a little more diagnosing before going on the hunt for used 4wabs. The exception was because on the way home from work about an hour ago, I had 2 back-to-back instances of delayed 1-2 upshift again.:doh0715:
When I installed the jumpers last night I left the battery disconnected for 30 mins so the CPU should have reset. Therefore I just now checked the codes and got the same continuous memory codes that I've had since I got the truck 452(vss signal fault) and 628(excessive converter clutch slippage). I've already replaced the VSS and only 2 out of probably 500 shifts throughout my drives today were bad so im thinking something intermittent like the a wiring splice/connector.
Should I be concerned about the 628 code since I gotta drive it 800 miles on Thursday? I had always hoped that since the e4od is all electronic and since I knew that vss issues were causing the only other code, that the 628 code was erroneous...wishful thinking?
Since I cleaned up my jumpers this time last night, I have made 8 trips that covered 40 miles of city traffic. The whole time every shift was perfect, way better than at any time since I got the truck a year ago. However, there was one exception that is making me consider doing a little more diagnosing before going on the hunt for used 4wabs. The exception was because on the way home from work about an hour ago, I had 2 back-to-back instances of delayed 1-2 upshift again.:doh0715:
When I installed the jumpers last night I left the battery disconnected for 30 mins so the CPU should have reset. Therefore I just now checked the codes and got the same continuous memory codes that I've had since I got the truck 452(vss signal fault) and 628(excessive converter clutch slippage). I've already replaced the VSS and only 2 out of probably 500 shifts throughout my drives today were bad so im thinking something intermittent like the a wiring splice/connector.
Should I be concerned about the 628 code since I gotta drive it 800 miles on Thursday? I had always hoped that since the e4od is all electronic and since I knew that vss issues were causing the only other code, that the 628 code was erroneous...wishful thinking?
yo Matt,
Ensure you have a full$ back guarantee if yard queen module is toasted. I went through 2 yard modules that were shot.. no $ back on any electrical part around here.
The two microprocessors burn in the sealed module.
"There are two different microprocessors controlling the program sequence. One of the microprocessors provides mostly a monitoring function the other controlling the ABS system. The relay in the ABS module activates the ABS brake pressure pump (HCU) and in this way the ABS brake pressure pump is supplied with voltage. When voltage peaks occur the diodes integrated in the relay assembly protect against polarity reversal and over-voltage"
Ensure you have a full$ back guarantee if yard queen module is toasted. I went through 2 yard modules that were shot.. no $ back on any electrical part around here.
The two microprocessors burn in the sealed module.
"There are two different microprocessors controlling the program sequence. One of the microprocessors provides mostly a monitoring function the other controlling the ABS system. The relay in the ABS module activates the ABS brake pressure pump (HCU) and in this way the ABS brake pressure pump is supplied with voltage. When voltage peaks occur the diodes integrated in the relay assembly protect against polarity reversal and over-voltage"
To me, automatic transmissions are magic boxes - I've never attempted to understand the details of what goes on inside, so I can't help diagnose one. But for any code, the first step is to confirm that the indicated symptom actually exists. If your converter isn't actually slipping, then it's a spurious code, and diagnosis would happen OUTSIDE the transmission.
Thanks Miesk5 and Steve83. I'm with ya about the majic box aspect since the transmission is the one part on the ford trucks I've had that I have not fully disassembled and repaired. I'll take a close look at those 2 microprocessors whenever I dissect the module.
Half way thru my drive to work just now the hard/ delayed shifts came back and I still have the jumpers in place/module unplugged. I tried turning the ignition off at red lights to reset limp but the hard/delayed shifts persisted.
i get the impression that once a vss signal fault is detected, that limp mode kicks in and stays on for the rest of the drive even if there's no additional faults . Is that true?
I read many posts about e4OD limp mode but I didn't see any specific info such as, once e4od limp is triggered how long does it stay on for?
![Image]()
Half way thru my drive to work just now the hard/ delayed shifts came back and I still have the jumpers in place/module unplugged. I tried turning the ignition off at red lights to reset limp but the hard/delayed shifts persisted.
i get the impression that once a vss signal fault is detected, that limp mode kicks in and stays on for the rest of the drive even if there's no additional faults . Is that true?
I read many posts about e4OD limp mode but I didn't see any specific info such as, once e4od limp is triggered how long does it stay on for?
yo Matt,
If all the shifts are hard, PCM is going into limp mode that causes E4OD to shift hard because the pressures are increased.
PCM goes into limp mode when it senses an error in the transmission shifting or electrical system.
The most common cause for this is the Manual Lever Position (MLPS) also called Transmission Range (TR) Sensor. This is the sensor that is bolted to the drivers side of the transmission case with the shift lever arm going through the center of the sensor.
Try disconnecting the battery for 15 minutes with the headlamps on. This should clear the limp mode and return the transmission to normal shift strategy. If it does then the problem is intermittent.If it still shifts hard then the fault is continuously occurring. It is possible that there is another input/output signal problem, but 99% of the time it is the MLPS/TR sensor especially if it clears limp mode proving the problem is intermittent.
happens when the vehicle computer recognizes a problem in it's logic. When an expected signal value from a sensor is sent to the computer and is not within the computer's programmed specifications, "secondary" programs are activated by the computer to strive to protect the transmission from damage the improper sensor signal might cause to occur.
In other words, the computer is always expecting certain signal values from certain sensors i.e. the temperature sensor, the speed sensor, the throttle position sensor, etc. As long as these signals are what it would normally expect for the conditions and is normal based on all the other signals it is receiving from other sensors, it acts normally and accordingly.
If the computer, all of a sudden, receives some crazy signal from one of the sensors that is out of the normal range expected from this sensor, it will go to "emergency" or "secondary" measures.
These emergency measures vary depending on the severity of the defective signal. All this is preprogrammed into the computer's logic by the manufacturer. The manufacturer has decided that as long as a certain parameter of a particular signal is sent from a sensor to the computer, all is well. The manufacturer decided that if this signal is higher than their highest parameter or lower than their lowest parameter, something is wrong with that sensor and the computer should make someone aware of the situation and take action to try to "save" the vehicle systems or powertrain.
Perhaps the computer will simply cause the "check engine" light to come on. The signal variation wasn't severe or critical to cause any mechanical failures but the vehicle's operator is made aware that he or she should have the vehicle checked out electronically to see if a minor sensor has broken down or is starting to send the odd irratic signal. This type of condition is commonly referred to as a "soft code". Normal functions are not affected but if the repair is not made, performance or fuel efficiencies might suffer. Perhaps the sensor only malfunctioned one time and all other times was fine. This might be an early warning of a sensor that is beginning to fail or has a loose connector or connection.
Other times the signal needed to perform operations normally is so far out of specification that the computer has no choice but to go into survival mode. With transmissions, the computer will cause the internal tranny fluid line pressure to default to high to protect clutches and bands. The transmission also turns off the shift solenoids to cause the unit to default to a single gear, usually second or third. All normal instructions to control line pressure are overridden so a hazardous "slipping condition" cannot occur easily. This theoretically is so that the vehicle's driver can get the damaged vehicle to the next town for repairs. This condition is commonly called "Limp Mode" for this reason. You limp to the next town in second or third gear only, at full line pressure so the tranny guts won't slip on your trip in.
By the way, interestingly and just as a side note, if the cable harness going to your transmission was ever to become detached, severed or damaged, your transmission would also go to "limp mode".
The vehicle's computer would immediately sense that it has lost contact with the transmission and would set the codes and send "limp mode" signals to the tranny. But because the harness is severed between the computer and the transmission, no computer signals will reach the transmission. These sent signals, however, would have had the identical affect on the transmission as what taking away supplied power to the shift and line pressure solenoids has as in the case of a transmission harness being detached or cut. Due to the engineered voltage strategies of the solenoids, the transmission simply defaults to a single gear and line pressure defaults to high, all in order to "limp" you home.
A Throttle Position Sensor that improperly sends a reading that it is wide open when in fact it is physically closed would be detected by the computer when it compared this reading with the vehicle speed sensor that perhaps is showing very slow vehicle speed. The signal, by itself can't be considered wrong but when put against all the other sensor signals of the system might cause a computer concern. The computer, at this point, unable to "trust" the collection of signals because together they are not making sense in it's logic, will simply go to limp mode in the transmission to protect it and make the operator aware that something is wrong with one of the sensors and a mechanic's attention is needed to correct the situation.
Source: by Greg O at autotransinc.com via webarchive.org
DS1 DIAGNOSTIC TROUBLE CODES (DTCS) 29 AND 452: CHECK PSOM RESISTANCE
628; TG90 PERFORM DRIVE CYCLE TEST
here are excerpts;
"...
Possible causes:
â—ľIntermittent harness continuity.
â—ľDamaged Manual Lever Position (MLP) Sensor.
â—ľDamaged shift solenoid.
â—ľWorn friction elements.
•Enter Key On Engine Off Continuous Monitor Diagnostic Test Mode (DTM). Refer to Quick Test Appendix, Section 5A.
•Observe VOM or STAR Tester LED for an indication of a fault while performing the following:
â—ľWiggle, shake or bend a small section of the Powertrain Control Module (PCM) vehicle harness while working toward the dash panel, PCM and transmission connectors.
Is a fault indicated?
Yes DISCONNECT and INSPECT connector and harness wires. SERVICE as necessary. CLEAR Continuous Memory (REFER to Quick Test Appendix, Section 5A). RERUN Quick Test. If the concern remains, REFER to appropriate Transmission Group in Service Manual for possible internal transmission damage.
No REFER to appropriate Transmission Group in the Service Manual
read more..
------
fyi & posterity;
"...One of the most-difficult problems to diagnose on a Ford car or truck is a sudden neutral condition while the vehicle is cruising in 4th gear. Now this can have a number of causes, depending on which transmission is in the car or truck, but the cause we are going to discuss here is that #(~! *&A% Manual Lever Position Sensor – that’s right, the old MLPS. This sensor is responsible for more malfunctions than any other sensor in the system, and the kicker is that it seldom stores a code 67 or 634. Actually there is a standing joke in our industry that says, “You got a problem with a Ford, change the MLPS; it fixes everything,” which ain’t that funny because it’s not that far from the truth. Some of the problems the MLPS can cause are wrong gear starts, TCC hunting, no 4th gear, engine stalling, high or erratic line pressure and the problem that this article is about – a sudden neutral condition. Whether the MLPS is attached to an E4OD, AXODE, AODE or CD4E, the operating characteristics are the same. What that means is the MLPS is classified as a step-down resistor. The MLPS is supplied 5 volts from the computer as a reference voltage, and as the shift lever is moved from park toward manual low, the voltage in each gear-shift position will decrease as shown in Figure 1. The MLPS also can be checked for correct resistance, also shown in Figure 1. This way, if the resistance checked good on the bench but the voltage does not check good in the vehicle, you know there must be a wiring or ground problem. I know what you are thinking: You replace the MLPS on every job you do, so why should you check the resistance on a new part? Well, that’s fine, but one thing has become very clear lately: NEW DOES NOT MEAN GOOD! Now, let’s get to the meat of the problem. As you can see in Figure 1, the voltage in the drive/overdrive position can be 1.88 to 2.30 volts. The O.D. Cancel button, on those vehicles equipped with one, has no effect on the voltage seen in the drive position, nor does it matter whether the vehicle has a gas or diesel engine. This would be the voltage seen in the D or D position if it were available on the scan-tool screen in the data mode. Unfortunately, this information is not always available, and this “glitch” may occur faster than the scan-tool’s update capability so the voltage jump would be missed. Therefore, a digital multimeter must be used to monitor this voltage. This is of the utmost importance in diagnosing the sudden-neutral condition. This voltage should be monitored when the neutral condition occurs by placing the multimeter’s positive lead to computer terminal 30 if it is an EEC-IV system, as illustrated in Figure 2, or to terminal 64 if it is an EEC-V system. This wire is light blue/yellow on all applications except vehicles with the CD4E. On these the signal wire is red/black. Now, here is where this gets a little involved. The negative lead of the multimeter should be placed at the MLPS signal-return ground terminal at the MLPS. The reason is that the ground circuit for the MLPS can be shared by as many as FIVE other sensors, as seen in the wiring diagram in Figure 2. This means that there are factory splices in this ground circuit. If you check this ground at computer terminal 46 for the EEC- IV or computer terminal 91 for the EEC-V, the ground may check good but could be bad at the MLPS if there is a problem on the MLPS side of the splice, as also can be seen in the wiring diagram in Figure 2. The ground-circuit wire for 1989-90 F- and E-series trucks is black/white; all other vehicles use a gray/red ground wire except for CD4E applications, on which the ground wire is black/blue. Once the multimeter is connected to these circuits, as seen in Figure 3, place the meter where it can be seen while driving. When the transmission suddenly neutrals, be sure to have someone observe the multimeter, or use the meter’s MIN/MAX feature to record the highest and lowest voltage readings that occurred in the circuit. If the voltage jumps toward 3 volts as shown in Figure 3, and at that very moment the transmission neutrals, either the MLPS is faulty or the MLPS ground circuit is poor. Under normal conditions, this voltage reading SHOULD NOT CHANGE! When the voltage jumps toward 3 volts, this indicates a neutral-shift- lever position to the processor. This confuses the computer’s logic system, and therefore the computer is unable to fire the shift solenoids correctly (I think), and – BAM – you have a sudden-neutral condition. Why does the voltage jump because of a poor ground? The poorer the ground, the higher the resistance will be in that ground circuit. The higher resistance will cause the voltage in the overdrive or drive position to rise toward the 5-volt reference voltage, much like putting a bend in a garden hose would raise the pressure in the hose behind the bend. Ground- circuit integrity can be verified by placing the positive multimeter lead to the MLPS ground terminal at the MLPS and the negative multimeter lead to the negative battery post, as seen in Figure 4. With the multimeter set to DC volts and the engine running, the maximum voltage should be 0.1 volt. If more than 0.1 volt is seen on this ground circuit, it is NOT a good ground. In order to correct this condition, cut the ground wire close to the MLPS, attach it to a known good ground and recheck as previously described. Two things must be remembered here. One is that the return electricity will seek the path of least resistance. This path MUST be the ground circuit, NOT your multimeter. That’s why you should see a maximum of 0.1 volt on any 5-volt-reference ground circuit; 0.3 is acceptable on a 12-volt-reference voltage supply. The second thing to remember is that most electrical- fault phone calls I receive on the ATSG helpline are ground-related problems, so be sure to use the voltage-drop method of checking grounds as described. It may help to prevent you from falling into this trap..." See Diagrams & instructions
Source: by Pete L at
http://web.archive.org/web/20030510...p://www.transonline.com/transdigest/magazines/1998-10/Shift Pointers/index.html
If all the shifts are hard, PCM is going into limp mode that causes E4OD to shift hard because the pressures are increased.
PCM goes into limp mode when it senses an error in the transmission shifting or electrical system.
The most common cause for this is the Manual Lever Position (MLPS) also called Transmission Range (TR) Sensor. This is the sensor that is bolted to the drivers side of the transmission case with the shift lever arm going through the center of the sensor.
Try disconnecting the battery for 15 minutes with the headlamps on. This should clear the limp mode and return the transmission to normal shift strategy. If it does then the problem is intermittent.If it still shifts hard then the fault is continuously occurring. It is possible that there is another input/output signal problem, but 99% of the time it is the MLPS/TR sensor especially if it clears limp mode proving the problem is intermittent.
happens when the vehicle computer recognizes a problem in it's logic. When an expected signal value from a sensor is sent to the computer and is not within the computer's programmed specifications, "secondary" programs are activated by the computer to strive to protect the transmission from damage the improper sensor signal might cause to occur.
In other words, the computer is always expecting certain signal values from certain sensors i.e. the temperature sensor, the speed sensor, the throttle position sensor, etc. As long as these signals are what it would normally expect for the conditions and is normal based on all the other signals it is receiving from other sensors, it acts normally and accordingly.
If the computer, all of a sudden, receives some crazy signal from one of the sensors that is out of the normal range expected from this sensor, it will go to "emergency" or "secondary" measures.
These emergency measures vary depending on the severity of the defective signal. All this is preprogrammed into the computer's logic by the manufacturer. The manufacturer has decided that as long as a certain parameter of a particular signal is sent from a sensor to the computer, all is well. The manufacturer decided that if this signal is higher than their highest parameter or lower than their lowest parameter, something is wrong with that sensor and the computer should make someone aware of the situation and take action to try to "save" the vehicle systems or powertrain.
Perhaps the computer will simply cause the "check engine" light to come on. The signal variation wasn't severe or critical to cause any mechanical failures but the vehicle's operator is made aware that he or she should have the vehicle checked out electronically to see if a minor sensor has broken down or is starting to send the odd irratic signal. This type of condition is commonly referred to as a "soft code". Normal functions are not affected but if the repair is not made, performance or fuel efficiencies might suffer. Perhaps the sensor only malfunctioned one time and all other times was fine. This might be an early warning of a sensor that is beginning to fail or has a loose connector or connection.
Other times the signal needed to perform operations normally is so far out of specification that the computer has no choice but to go into survival mode. With transmissions, the computer will cause the internal tranny fluid line pressure to default to high to protect clutches and bands. The transmission also turns off the shift solenoids to cause the unit to default to a single gear, usually second or third. All normal instructions to control line pressure are overridden so a hazardous "slipping condition" cannot occur easily. This theoretically is so that the vehicle's driver can get the damaged vehicle to the next town for repairs. This condition is commonly called "Limp Mode" for this reason. You limp to the next town in second or third gear only, at full line pressure so the tranny guts won't slip on your trip in.
By the way, interestingly and just as a side note, if the cable harness going to your transmission was ever to become detached, severed or damaged, your transmission would also go to "limp mode".
The vehicle's computer would immediately sense that it has lost contact with the transmission and would set the codes and send "limp mode" signals to the tranny. But because the harness is severed between the computer and the transmission, no computer signals will reach the transmission. These sent signals, however, would have had the identical affect on the transmission as what taking away supplied power to the shift and line pressure solenoids has as in the case of a transmission harness being detached or cut. Due to the engineered voltage strategies of the solenoids, the transmission simply defaults to a single gear and line pressure defaults to high, all in order to "limp" you home.
A Throttle Position Sensor that improperly sends a reading that it is wide open when in fact it is physically closed would be detected by the computer when it compared this reading with the vehicle speed sensor that perhaps is showing very slow vehicle speed. The signal, by itself can't be considered wrong but when put against all the other sensor signals of the system might cause a computer concern. The computer, at this point, unable to "trust" the collection of signals because together they are not making sense in it's logic, will simply go to limp mode in the transmission to protect it and make the operator aware that something is wrong with one of the sensors and a mechanic's attention is needed to correct the situation.
Source: by Greg O at autotransinc.com via webarchive.org
DS1 DIAGNOSTIC TROUBLE CODES (DTCS) 29 AND 452: CHECK PSOM RESISTANCE
628; TG90 PERFORM DRIVE CYCLE TEST
here are excerpts;
"...
Possible causes:
â—ľIntermittent harness continuity.
â—ľDamaged Manual Lever Position (MLP) Sensor.
â—ľDamaged shift solenoid.
â—ľWorn friction elements.
•Enter Key On Engine Off Continuous Monitor Diagnostic Test Mode (DTM). Refer to Quick Test Appendix, Section 5A.
•Observe VOM or STAR Tester LED for an indication of a fault while performing the following:
â—ľWiggle, shake or bend a small section of the Powertrain Control Module (PCM) vehicle harness while working toward the dash panel, PCM and transmission connectors.
Is a fault indicated?
Yes DISCONNECT and INSPECT connector and harness wires. SERVICE as necessary. CLEAR Continuous Memory (REFER to Quick Test Appendix, Section 5A). RERUN Quick Test. If the concern remains, REFER to appropriate Transmission Group in Service Manual for possible internal transmission damage.
No REFER to appropriate Transmission Group in the Service Manual
read more..
------
fyi & posterity;
"...One of the most-difficult problems to diagnose on a Ford car or truck is a sudden neutral condition while the vehicle is cruising in 4th gear. Now this can have a number of causes, depending on which transmission is in the car or truck, but the cause we are going to discuss here is that #(~! *&A% Manual Lever Position Sensor – that’s right, the old MLPS. This sensor is responsible for more malfunctions than any other sensor in the system, and the kicker is that it seldom stores a code 67 or 634. Actually there is a standing joke in our industry that says, “You got a problem with a Ford, change the MLPS; it fixes everything,” which ain’t that funny because it’s not that far from the truth. Some of the problems the MLPS can cause are wrong gear starts, TCC hunting, no 4th gear, engine stalling, high or erratic line pressure and the problem that this article is about – a sudden neutral condition. Whether the MLPS is attached to an E4OD, AXODE, AODE or CD4E, the operating characteristics are the same. What that means is the MLPS is classified as a step-down resistor. The MLPS is supplied 5 volts from the computer as a reference voltage, and as the shift lever is moved from park toward manual low, the voltage in each gear-shift position will decrease as shown in Figure 1. The MLPS also can be checked for correct resistance, also shown in Figure 1. This way, if the resistance checked good on the bench but the voltage does not check good in the vehicle, you know there must be a wiring or ground problem. I know what you are thinking: You replace the MLPS on every job you do, so why should you check the resistance on a new part? Well, that’s fine, but one thing has become very clear lately: NEW DOES NOT MEAN GOOD! Now, let’s get to the meat of the problem. As you can see in Figure 1, the voltage in the drive/overdrive position can be 1.88 to 2.30 volts. The O.D. Cancel button, on those vehicles equipped with one, has no effect on the voltage seen in the drive position, nor does it matter whether the vehicle has a gas or diesel engine. This would be the voltage seen in the D or D position if it were available on the scan-tool screen in the data mode. Unfortunately, this information is not always available, and this “glitch” may occur faster than the scan-tool’s update capability so the voltage jump would be missed. Therefore, a digital multimeter must be used to monitor this voltage. This is of the utmost importance in diagnosing the sudden-neutral condition. This voltage should be monitored when the neutral condition occurs by placing the multimeter’s positive lead to computer terminal 30 if it is an EEC-IV system, as illustrated in Figure 2, or to terminal 64 if it is an EEC-V system. This wire is light blue/yellow on all applications except vehicles with the CD4E. On these the signal wire is red/black. Now, here is where this gets a little involved. The negative lead of the multimeter should be placed at the MLPS signal-return ground terminal at the MLPS. The reason is that the ground circuit for the MLPS can be shared by as many as FIVE other sensors, as seen in the wiring diagram in Figure 2. This means that there are factory splices in this ground circuit. If you check this ground at computer terminal 46 for the EEC- IV or computer terminal 91 for the EEC-V, the ground may check good but could be bad at the MLPS if there is a problem on the MLPS side of the splice, as also can be seen in the wiring diagram in Figure 2. The ground-circuit wire for 1989-90 F- and E-series trucks is black/white; all other vehicles use a gray/red ground wire except for CD4E applications, on which the ground wire is black/blue. Once the multimeter is connected to these circuits, as seen in Figure 3, place the meter where it can be seen while driving. When the transmission suddenly neutrals, be sure to have someone observe the multimeter, or use the meter’s MIN/MAX feature to record the highest and lowest voltage readings that occurred in the circuit. If the voltage jumps toward 3 volts as shown in Figure 3, and at that very moment the transmission neutrals, either the MLPS is faulty or the MLPS ground circuit is poor. Under normal conditions, this voltage reading SHOULD NOT CHANGE! When the voltage jumps toward 3 volts, this indicates a neutral-shift- lever position to the processor. This confuses the computer’s logic system, and therefore the computer is unable to fire the shift solenoids correctly (I think), and – BAM – you have a sudden-neutral condition. Why does the voltage jump because of a poor ground? The poorer the ground, the higher the resistance will be in that ground circuit. The higher resistance will cause the voltage in the overdrive or drive position to rise toward the 5-volt reference voltage, much like putting a bend in a garden hose would raise the pressure in the hose behind the bend. Ground- circuit integrity can be verified by placing the positive multimeter lead to the MLPS ground terminal at the MLPS and the negative multimeter lead to the negative battery post, as seen in Figure 4. With the multimeter set to DC volts and the engine running, the maximum voltage should be 0.1 volt. If more than 0.1 volt is seen on this ground circuit, it is NOT a good ground. In order to correct this condition, cut the ground wire close to the MLPS, attach it to a known good ground and recheck as previously described. Two things must be remembered here. One is that the return electricity will seek the path of least resistance. This path MUST be the ground circuit, NOT your multimeter. That’s why you should see a maximum of 0.1 volt on any 5-volt-reference ground circuit; 0.3 is acceptable on a 12-volt-reference voltage supply. The second thing to remember is that most electrical- fault phone calls I receive on the ATSG helpline are ground-related problems, so be sure to use the voltage-drop method of checking grounds as described. It may help to prevent you from falling into this trap..." See Diagrams & instructions
Source: by Pete L at
http://web.archive.org/web/20030510...p://www.transonline.com/transdigest/magazines/1998-10/Shift Pointers/index.html
yo Matt,
Here is Ford's info; sans your specific issues and DTCs
Electrical Schematic — 94 Bronco/F Series E4OD SFI
See attachment below.
And a typical Ford explantaion of Failure Mode Effects Management (FMEM) or Hardware Limited Operation Strategy (HLOS)
TSB: 88-05-07
http://www.revbase.com/BBBMotor/TSb/DownloadPdf?id=23128
Excerpts;
"...CHECK ENGINE light will come on while engine is operating in Failure Mode Effects Management (FMEM) or Hardware Limited Operation Strategy (HLOS) modes. The light will stay on as long as the fault causing it is present. In FMEM mode, the computer is receiving a sensor signal that is outside the limits set by the calibration strategy. In this mode, the computer uses an alternate strategy to maintain reasonable vehicle operation in spite of the fault. The following chart lists the system faults which will turn on the CHECK ENGINE light in this mode. The error code associated with this system fault is stored in Keep Alive Memory (KAM). If the fault is no longer present, the light will turn off and vehicle will return to normal vehicle strategy. The error code stored when the light was on was not erased. This code is one of the continuous error codes and can be accessed by running the KOEO self-test.
HLOS mode is used when the system fault(s) is too extreme for the FMEM mode to handle. In HLOS mode, all software operations have stopped and the computer is running on hardware control only. The default strategy for this mode has a minimal calibration just to allow the vehicle to operate until it can be serviced.
IN HLOS MODE YOU WILL NOT GET ERROR CODES..."
===========
And in your year from 1994 Powertrain Control/Emissions Diagnosis Manual;
"Malfunction Indicator Lamp (MIL)—All Applications Except Continental
The Malfunction Indicator Lamp (MIL) is intended to alert the driver of certain malfunctions in the EEC-IV system. The MIL is a light in the dash that reads either "CHECK ENGINE" or "SERVICE ENGINE SOON." If the light is on, the driver of the vehicle should take the car in for service as soon as possible.
Note: It is not necessary to immediately turn the engine off and have the vehicle towed when the MIL comes on.
The MIL will come on while the engine is operating in Failure Mode Effects Management (FMEM) or Hardware Limited Operation Strategy (HLOS) modes. The light will stay on for at least 10 seconds, then stay on as long as the fault causing it is present. If the MIL flashes quickly (less than 10 seconds), the MIL circuit should be checked for concerns. Refer to Quick Test.
In FMEM mode, the PCM is receiving a sensor signal that is outside the limits set by the calibration strategy. In this mode, the PCM uses an alternate engine control strategy to maintain reasonable vehicle operation in spite of the fault. The DTC associated with this fault is stored in Keep Alive Memory (KAM). If the fault is no longer present, the light will turn off and the vehicle will return to the normal vehicle strategy. The DTC stored when the light was on is kept in Continuous Memory for the next 80 warm-up cycles (40 cycles on some applications) and then erased. This Continuous Memory DTC can be accessed by running the Key On Engine Off Self-Test.
HLOS mode is used when the system fault(s) is too extreme for the FMEM mode to handle. In HLOS mode, all software operations have stopped and the PCM is running on hardware control only. The default strategy for this mode has a minimal calibration strictly to allow the vehicle to operate until it can be serviced.
Note: In HLOS mode Self-Test DTCs will not be output."
Here is Ford's info; sans your specific issues and DTCs
Electrical Schematic — 94 Bronco/F Series E4OD SFI
See attachment below.
And a typical Ford explantaion of Failure Mode Effects Management (FMEM) or Hardware Limited Operation Strategy (HLOS)
TSB: 88-05-07
http://www.revbase.com/BBBMotor/TSb/DownloadPdf?id=23128
Excerpts;
"...CHECK ENGINE light will come on while engine is operating in Failure Mode Effects Management (FMEM) or Hardware Limited Operation Strategy (HLOS) modes. The light will stay on as long as the fault causing it is present. In FMEM mode, the computer is receiving a sensor signal that is outside the limits set by the calibration strategy. In this mode, the computer uses an alternate strategy to maintain reasonable vehicle operation in spite of the fault. The following chart lists the system faults which will turn on the CHECK ENGINE light in this mode. The error code associated with this system fault is stored in Keep Alive Memory (KAM). If the fault is no longer present, the light will turn off and vehicle will return to normal vehicle strategy. The error code stored when the light was on was not erased. This code is one of the continuous error codes and can be accessed by running the KOEO self-test.
HLOS mode is used when the system fault(s) is too extreme for the FMEM mode to handle. In HLOS mode, all software operations have stopped and the computer is running on hardware control only. The default strategy for this mode has a minimal calibration just to allow the vehicle to operate until it can be serviced.
IN HLOS MODE YOU WILL NOT GET ERROR CODES..."
===========
And in your year from 1994 Powertrain Control/Emissions Diagnosis Manual;
"Malfunction Indicator Lamp (MIL)—All Applications Except Continental
The Malfunction Indicator Lamp (MIL) is intended to alert the driver of certain malfunctions in the EEC-IV system. The MIL is a light in the dash that reads either "CHECK ENGINE" or "SERVICE ENGINE SOON." If the light is on, the driver of the vehicle should take the car in for service as soon as possible.
Note: It is not necessary to immediately turn the engine off and have the vehicle towed when the MIL comes on.
The MIL will come on while the engine is operating in Failure Mode Effects Management (FMEM) or Hardware Limited Operation Strategy (HLOS) modes. The light will stay on for at least 10 seconds, then stay on as long as the fault causing it is present. If the MIL flashes quickly (less than 10 seconds), the MIL circuit should be checked for concerns. Refer to Quick Test.
In FMEM mode, the PCM is receiving a sensor signal that is outside the limits set by the calibration strategy. In this mode, the PCM uses an alternate engine control strategy to maintain reasonable vehicle operation in spite of the fault. The DTC associated with this fault is stored in Keep Alive Memory (KAM). If the fault is no longer present, the light will turn off and the vehicle will return to the normal vehicle strategy. The DTC stored when the light was on is kept in Continuous Memory for the next 80 warm-up cycles (40 cycles on some applications) and then erased. This Continuous Memory DTC can be accessed by running the Key On Engine Off Self-Test.
HLOS mode is used when the system fault(s) is too extreme for the FMEM mode to handle. In HLOS mode, all software operations have stopped and the PCM is running on hardware control only. The default strategy for this mode has a minimal calibration strictly to allow the vehicle to operate until it can be serviced.
Note: In HLOS mode Self-Test DTCs will not be output."
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